Apparatus for quantitative determination of sulfur



May 26, 1959 w; K. Amas 2,888,332

APPARATUS FOR QUANTITATIVE DETERMINATIONl 0F ULFUR Filed may les.l 1955 v K103i ATTORNEYS.

United States Patent O APPARATUS FOR QUANTITATIVE DETERMINA- TION OF SULFUR William K. Aites, Pittsburgh, Pa., assgnor to Lindberg Engineering Company, Chicago, Ill., a corporation of Illinois Application May 16, 1955, Serial No. 508,452

8 Claims. (Cl. 23^253) This invention relates to an apparatusv for quantitatively determining sulfur in samples of hydrocarbons, ferrous metals or other materials which contain sulfur in small quantities. f

Apparatus of this type generally' includes a combustion tube in which the sample is volatilized by a high-frequency induction coil surrounding the tube, means yfor llowing oxygen through the tube to oxidize the gases evolved, and suitable absorption means for separating the oxides of sulfur from the eilluent gases. It has been found that frequently the sample is not completely oxidized. Particularly in the analysis of liquid hydro-v carbons, the sample rapidly vaporizes and the lighter fractions escape from the cupelet Without being come pletely burned or combusted. If all of the sulfur carried over into the absorbent is not oxidized, the analytical results are low.

ln accordance with this invention a secondary heater is disposed within the combustion tube above the crucible containing the sample to be analyzed. The heater may take the form of a metal Wire halo mounted above the mouth of the crucible within the high-frequency eldor may be an electrically resistant heating element, such as Nichrome wire or Kanthal A wire, connected to 'an external source of electrical energy, for example, a 115 volt alternating current line. The presence of the secondary heater within the combustion tube will insure elevation of the temperature of the effluent gases to the point where complete combustion is effected. The secondary heater may be made from a material that will catalyze the oxidation reaction as Well as supply heat for the reaction.

It is, therefore, the primary object of this invention to provide an improved apparatus for analyzing samples for sulfur in which the sulfur is completely oxidized, thus giving highly accurate results.

Another object is to provide an apparatus of the type described in which the crucible holding the unknown, and the secondary heater above the crucible, are both embraced by a high-frequency coil outside the combustion tube.

Another object is to provide novel means for suspending the secondary heater in the combustion tube. Y

Other objects and advantages of this invention will become apparent from the following description when read in conjunction with the accompanying drawing, in which:

Figure 1 is a semi-diagrammatic view of an apparatus constructed in accordance with this invention;

Figure 2 shows a portion of `the combustion tube containing a modified form of secondary heater;

Figure 3 is a sectional view taken along line 3-3 of Figure 2;and

Figure 4 is a view similar to Figure 2 showing another construction for the secondary heater.

Referring to the drawing, the combustion tube 10, having an opening 11 in the lower end, serves to conne the crucible or cupelet 50 which holds the'sample of un- Patented May 26, 1959 HCC known X. The sample may be steel, rubber, oil, or other material containing sulfur to be quantitatively determined. The upper end of the tube 10 terminates in a neck 14 to which a exible tube 16 is connected for conducting the effluent combustion gases to the absorption portion of the apparatus. A small `tube 13 connects to the side wall of the tube 10 at its lower end for introducing oxygen into the combustion tube. The tube 10 is preferably made from quartz or a refractory glass which contains a very high quantity lof silica. l have found that a glass containing 96% silica sold under the narne Vycor is very satisfactory. High silica glasses of this type will resist temperatures in the range of 2.500" to 3000" F., which are attained in the combustion of samples. The flexible tube 16 connects to a sulfur titration vessel 18 through a trap 17 to permit the eilluent gases to bubble through the absorbent liquid 22 in the vessel 18. A burette 20' is mounted above the open end of the vessel 18 for adding measured quantities of titrating liquid, such as potassium iodate. The analysis for sulfur is carried out in accordance with the standard ASTM iodiometric method r(E30-47). l

A refractory cylinder or pedestal 24 mounted on an elevator platform 26 serves to support the crucible 50 within the combustion tube. The platform 26 is iixed to the end of the rod 28 which slides vertically in the bearing 30 fixed to a suitable support (not shown). Suitable locking means may be provided for holding the crucible 50 in an elevated position. A resilient seal 25, such as an asbestos gasket, between the platform 26 and the lower lip of the tube 10 serves to seal the tubecompletely when the pedestal 24 is in elevated position.

For heating the sample and the secondary heater 42, a high-frequency induction coil embraces the upper portion of the combustion tube 10 to induce current in the y conductive material placed in the crucible with the sarnbottom ofthe crucible before the sample is poured in.'

ple. Where the unknown X is steel or similar conductive material, it will heat up in the high-frequency eld and no additional source of heat need be provided within the crucible. However, where the sample to be vanalyzed is a hydrocarbon, not affected by the high-frequency field, materials such as Plastiron (hydrogen reduced iron having a carbon content of less than .01% and a sulfur content of less than 008%), are placed in the crucible with the sample. in the high-frequency eld the Plastiron becomes very hot and volatilizes the sample. Porous ceramic cover 52 may be placed over the crucible and may contain a hole S3 through which the gases may escape'more rapidly than through the pores of the cover, but yet at a controlled rate.

The secondary heater consists of several turns of wire 43 embedded in a porous ceramic plug 42 which is of such diameter as to slide easily up the combustion tube 10. A coil spring 44, mounted transversely through an opening in the plug 42, is adapted to bear against the side walls of the tube 10 to hold the plug in any desired position by friction. The wire 43 may be a nickel-chromium alloy, platinum, copper, or similar metal. The plug 42 is made from a very porous refractory material, such as cellular silica. An insulating brick sold under the trade v name Armstrongs A-25 has been found to be very satisfactory. The pores are large enough so that little resistance is oered to the upwardly flowing gases.

If desired, in analyzing liquid hydrocarbons, a bedding material such as Alundum granules may be placed in the The sample adheres to the surface of the Alu-ndum granules and does not get down into the pores of the crucible Where it is more diflicult to volatilize. A detailed method for analyzing particularly for hydrocarbons is disclosed in the copending application of Stanley I. Mack, Serial No.

3 473,230, led December 6, 1954, now United States Patent No. 2,754,178.

In operating the apparatus, a measured quantity of the unknown sample is placed within thecrucible 50 and the porous ceramic cover 52 is placed thereover. This cover prevents the sample from volatilizing too rapidly. The opening 53 through the cover may be varied in size to control further the rate of volatilization. The Crucible is then placed on the pedestal 24 of the combustion apparatus and elevated into the tield of the conduction coil 40 by raising and clamping the rod 28 within the bearing 30. The flow of oxygen introduced through the tube 13 is initiated and the high-frequency coil is energized. The sample in the Crucible is volatilized either by reason of its being conductive, or being in Contact with conductive Plastiron, and passes upwardly through the porous cover 52. Because the halo wire 43 is within the high-frequency field, it becomes hot and any unoxidized sulfur in the eluent gases is oxidized as it passes the halo. The porous plug 42 in which the halo is mounted insures contact of the effluent gases with the wire by retarding the rate of flow and diffusing the gases. This is an important feature of this form of the invention. It will be understood that the halo may also be made from a material which serves as a catalyst for the oxidation of sulfur, providing, of course, it is also susceptible to attaining an elevated temperature within the energized high-frequency coil. The volatilized gases ow through the tube 16, trap 17 and up through the absorbing liquid 22 in the vessel 18. The absorbent may be a very dilute solution of hydrochloric acid containing starch as an indicator. rl`he amount of sulfur may be calculated from the amount of standard potassium iodate required to reach the end point.

As shown in Figure 2, the secondary heater need not depend upon the high-frequency coil for heating the same. The secondary heater, here illustrated, consists of a Nichrome wire coil 60, disposed within slots 62 of a ceramic bar 63, Figure 3. Leads 65, 66 from the coil 60 extend through the wall of the tube and connect to a 115 volt A.C. line. This resistance heater serves the same purpose as the halo within the high-frequency lield shown in Figure 1. Only the Crucible 50 is within the shortened high-frequency coil 67.

Another form of the secondary heater of Figure 1 is shown in Figure4. Porous ceramic plug 70, containing a coil spring 71, is similar to the plug 42 of Figure 1. However, instead of enclosing the wire halo within the porous plug itself, the halo extends from the bottom thereof in the form of a coil 74. The coil is suspended directly over the Crucible in alignment with the opening 53 in the cover 52 so that the volatilized material ows through the coil.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. In an apparatus for determining the sulfur content of an unknown sample of material containing sulfur, said apparatus being of the type comprising a Crucible for holding the sample, a combustion tube enclosing said Crucible, means for passing oxygen through said tube, a high-frequency coil embracing the portion of the tube surrounding the Crucible, and means connecting with the combustion tube for absorption of oxidized sulfur,

the improvement consisting of a secondary heater made of Conductive material mounted above the mouth of the Crucible.

2. In an apparatus for determining the sulfur content of an unknown sample of material Containing sulfur, said apparatus being of the type comprising a Crucible for holding the sample, a combustion tube enclosing said Crucible, means for passing oxygen through said tube, a high-frequency coil embracing a portion of the tube surrounding the Crucible and space above the Crucible, and means connecting with the combustion tube for absorption aeeesa of oxidized sulfur, the improvement consisting of a secondary heater made of conductive material mounted above the mouth of the Crucible within the high-frequency coil.

3. In an apparatus for determining the sulfur content of an unknown sample of material Containing sulfur, said apparatus being of the type Comprising a Crucible for holding the sample, a combustion tube enclosing said Crucible, means for passing oxygen through said tube, a high-frequency coil embracing only the portion of the tube surrounding the Crucible, and means connecting with the combustion tube for absorption of oxidized sulfur, the improvement consisting of a secondary heater mounted above the Crucible consisting of an electrical resistance element connected to an external power source.

4. In an apparatus for determining the sulfur content of an unknown sample of material containing sulfur, said apparatus being of the type comprising a Crucible for holding the sample, a combustion tube enclosing said Crucible, means for passing oxygen through said tube, a high-frequency coil embracing a portion of the tube surrounding the Crucible and space above the Crucible, and means connecting with the combustion tube for absorption of oxidized sulfur, the improvement consisting of a secondary heater mounted within the high-frequency coil above the Crucible comprising a conductive metal which catalyzes the oxidation of sulfur.

5. In an apparatus for determining the sulfur content of an unknown sample of material containing sulfur, said apparatus being of the type comprising a Crucible for holding the sample, a combustion tube enclosing said Crucible, means for passing oxygen through said tube, a high-frequency coil embracing a portion of the tube surrounding the Crucible and space above the Crucible, and means connecting with the combustion tube for absorption of oxidized sulfur, the improvement consisting of a secondary heater comprising a plug of porous gas-permeable refractory ceramic material disposed within said tube above the mouth of the Crucible and within the highfrequency coil, said plug Carrying a conductive wire halo.

6. In an apparatus for determining the sulfur content of an unknown sample of material containing sulfur, said apparatus being of the type comprising a Crucible for holding the sample, a combustion tube enclosing said Crucible, means for passing oxygen through said tube, a high-frequency coil embracing a portion of the tube surrounding the Crucible and space above the Crucible, and means connecting with the combustion tube for absorption of oxidized sulfur, the improvement consisting of a secondary heater comprising a plug of porous gas-permeable refractory ceramic material disposed within said tube above the mouth of the Crucible and within the high-frequency coil, said plughaving embedded therein a coil of conductive wire.

7. In an apparatus for determining the sulfur content of an unknown sample of material containing sulfur, said apparatus being of the type comprising a Crucible for holding the sample, a combustion tube enclosing said Crucible, means for passing oxygen through said tube, a high-frequency Coil embracing a portion of the tube surrounding the Crucible and space above the Crucible, and means connecting with the combustion tube for absorption of oxidized sulfur, the improvement consisting of a secondary heater comprising a plug of porous gaspermeable refractory ceramic material disposed within said tube above the mouth of the Crucible, said plug having a coiled conductive wire depending from the bottom thereof and within the high-frequency coil.

8. In an apparatus for determining the sulfur content of an unknown sample of material containing sulfur, said apparatus being of the type comprising a Crucible for holding the sample, a combustion tube enclosing said Crucible, means for passing oxygen through said tube, a high-frequency coil embracingv a portion of the tube surrounding the cruciblc and yspace above the Crucible, and means l` connecting with the combustion tube for absorption of oxidized sulfur, the improvement consisting of a secondary heater comprising a plug of porous ceramic material slidably disposed within said tube and carrying yieldable means for frictionally engaging the Wall of said tube to hold the plug in elevated position, said plug having a coil of conductive wire embedded therein beneath said yieldable means, said wire being disposed within the highfrequency coil.

References Cited in the le of this patent UNITED STATES PATENTS 1,795,926 Brace Mar. 10, 1931 5 2,661,386 Lundgren Dec. 1, 1953 2,673,228 Kistler Mar. 23, 1954 2,754,178 Mack July 10, 1956 OTHER REFERENCES lo Holler: Analytical Chemistry, vol. 23, No. 10, pages 1696 and 1697 (October 1951). 

1. IN AN APPARATUS FOR DETERMINING THE SULFUR CONTENT OF AN UNKNOWN SAMPLE OF MATERIAL CONTAINING SULFUR, SAID APPARATUS BEING OF THE TYPE COMPRISING A CRUCIBLE FOR HOLDING THE SAMPLE, A COMBUSTION TUBE ENCLOSING SAID CRUCIBLE, MEANS FOR PASSING OXYGEN THROUGH SAID TUBE, A HIGH-FREQUENCY COIL EMBRACING THE PORTION OF THE TUBE SURROUNDING THE CRUCIBLE, AND MEANS CONNECTING WITH THE COMBUSTION TUBE FOR ABSORPTION OF OXIDIZED SULFUR, THE IMPROVEMENT CONSISTING OF A SECONDARY HEATER MADE OF CONDUCTIVE MATERIAL MOUNTED ABOVE THE MOUTH OF THE CRUCIBLE. 